1. Field of the Invention
The present invention relates to an electrostatic breakdown protection circuit.
2. Description of the Prior Art
Shown in FIG. 5 is an example of a prior art electrostatic breakdown protection circuit, which includes a hot line 30 for carrying a data signal, an internal circuit 32 connected to the hot line 30 for receiving the data signal, a protection diode Da connected to ground and a protection diode Db connected to a power source line.
In operation, when a negative high surge voltage appears on the hot line 30, such a high voltage will be transmitted through diode Da to ground. Similarly, when a positive high surge voltage appears on the hot line 30, the high voltage will be transmitted through diode Db to the power source line. Therefore, the internal circuit 32 can be protected from a negative or positive surge voltage.
A protection circuit can be formed by connecting the gate bus lines or source bus lines, using a shortcircuit ring, an example of which is disclosed in Japanese Patent laid open publication No. 61-88557, published May 6, 1986. The shortcircuit ring is removed after the internal circuit is completed.
According to the prior art, one group of the protection diodes Da is connected to ground and another group of the protection diodes Db is connected to the power source line. Thus, the internal circuit can be easily shortcircuited to the ground or power source line, and thus it can be easily broken during the manufacturing thereof.
Also, when the shortcircuit ring is removed, the internal circuit 32 is not protected from positive or negative high voltages.